Point the proxy debugging doc at the method that builds the clients

The doc told the reader to add disableSslVerification() to
RustMatrixClientFactory.create(), which has not built the client for a long
time; getBaseClientBuilder() is where the chain lives, and it covers both the
login client and the restored session client.

It also only described the emulator's own proxy setting, while the app already
follows the device's global proxy through DefaultProxyProvider, which is the
only way to do this on a physical device.

docs/debug_proxying.md

@@ -9,13 +9,18 @@
     1) Set `127.0.0.1` as "Host name" and `8080` as "Port number".
     1) Click "Apply" and verify that "Proxy status" is "Success" and close the settings window.
        <img width="932" alt="Screenshot 2023-10-04 at 14 48 47" src="https://github.com/element-hq/element-x-android/assets/1273124/bf99a053-20b0-42a4-91d3-9602f709f684">
+    1) Alternatively, set the proxy on the device itself, which the app honours through `DefaultProxyProvider`, and which also works on a physical device:
+       ```
+       adb shell settings put global http_proxy 10.0.2.2:8080
+       ```
+       Use `adb shell settings delete global http_proxy` to remove it afterwards. On a physical device, replace `10.0.2.2` with the address of the machine running mitmproxy.
 1) Install the mitmproxy CA cert (this is needed to see traffic from java/kotlin code, it's not needed for traffic coming from native code e.g. the matrix-rust-sdk).
     1) Open the emulator Chrome browser app
     1) Go to the url `mitm.it`
     1) Follow the instructions to install the CA cert on Android devices.
        <img width="606" alt="Screenshot 2023-10-04 at 14 51 27" src="https://github.com/element-hq/element-x-android/assets/1273124/5f2b6f27-6958-4ea7-97fe-c7f06d105da5">
 1) Slightly modify the Element X app source code.
-    1) Go to the `RustMatrixClientFactory.create()` method.
+    1) Go to the `RustMatrixClientFactory.getBaseClientBuilder()` method, which builds every client the app creates, whether it is logging in or restoring a session.
     1) Add `.disableSslVerification()` in the `ClientBuilder` method chain.
 1) Build and run the Element X app. 
 1) Enjoy, you will see all the traffic in mitmproxy's web interface.